D&D
3e ~
base classes that I *will* play (the won't play list was too long): barbarian (1 or 2 lvl dip at best), cleric, crusader, druid, fighter (4 lvl dip at most), incarnate, psion, rogue, swordsage, totemist warblade, warlock, wilder, wizard
base classes that I haven't yet tried: anything from PHB II, Tome of Magic, probably forgetting something.
races ~
1/2 elf, 1/2 giant, 1/2 orc, goliaths, gnomes
1e and earlier: not interested.
2e: I might go back for nostalgia purposes.
4e: not interested. My last two (local) groups switched to 4e, I miss those guys
Non-D&D
Call of Cthulu & Paranoia: I don't like games where the PCs are automatically screwed.
Nothing else comes to mind for won't play.
DMing ~
I'll run 3e (3.75) and Star Wars (d20, haven't tried SAGA yet)